Vibrating device and image equipment having the same

ABSTRACT

A vibrating device includes a vibrator having a dust-screening member which is shaped like a plate as a whole and has at least one side that is symmetric with respect to a symmetry axis, and a vibrating member secured to the dust-screening member and configured to produce, at the dust-screening member, vibration having a vibrational amplitude perpendicular to a surface of the dust-screening member, and a hold and support member configured to hold and support the vibrator to a fixed member. The hold and support position by the hold and support member is arranged at position along a circle or ellipse concentric to the centroid of the vibrator such that peak ridges of the vibration having a vibrational amplitude perpendicular to the surface of the dust-screening member form closed loops.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2008-334693, filed Dec. 26, 2008;and No. 2009-263997, filed Nov. 19, 2009, the entire contents of both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image equipment having image formingelements such as an image sensor element or a display element, and alsoto a vibrating device designed to vibrate the dust-screening member thatis arranged at the front of each image forming element of such an imageequipment.

2. Description of the Related Art

As image equipment having image forming elements, there is known animage acquisition apparatus that has an image sensor element configuredto produce a video signal corresponding to the light applied to itsphotoelectric conversion surface. Also known is an image projector thathas a display element, such as liquid crystal element, which displays animage on a screen. In recent years, image equipment having such imageforming elements have been remarkably improved in terms of imagequality. If dust adheres to the surface of the image forming elementsuch as the image sensor element or display element or to the surface ofthe transparent member (optical element) that is positioned in front ofthe image forming element, the image produced will have shadows of thedust particles. This makes a great problem.

For example, digital cameras of called “lens-exchangeable type” havebeen put to practical use, each comprising a camera body and aphotographic optical system removably attached to the camera body. Thelens-exchangeable digital camera is so designed that the user can usevarious kinds of photographic optical systems, by removing thephotographic optical system from the camera body and then attaching anyother desirable photographic optical system to the camera body. When thephotographic optical system is removed from the camera body, the dustfloating in the environment of the camera flows into the camera body,possibly adhering to the surface of the image sensor element or to thesurface of the transparent member (optical element), such as a lens,cover glass or the like, that is positioned in front of the image sensorelement. The camera body contains various mechanisms, such as a shutterand a diaphragm mechanism. As these mechanisms operate, they producedust, which may adhere to the surface of the image sensor element aswell.

Projectors have been put to practical use, too, each configured toenlarge an image displayed by a display element (e.g., CRT or liquidcrystal element) and project the image onto a screen so that theenlarged image may be viewed. In such a projector, too, dust may adhereto the surface of the display element or to the surface of thetransparent member (optical element), such as a lens, cover glass or thelike, that is positioned in front of the display element, and enlargedshadows of the dust particles may inevitably be projected to the screen.

Various types of mechanisms that remove dust from the surface of theimage forming element or the transparent member (optical element) thatis positioned in front of the image sensor element, provided in suchimage equipment have been developed.

In an electronic image acquisition apparatus disclosed in, for example,U.S. 2004/0169761 A1, a ring-shaped piezoelectric element (vibratingmember) is secured to the circumferential edge of a glass plat shapedlike a disc (dust-screening member). When a voltage of a prescribedfrequency is applied to the piezoelectric element, the glass plat shapedlike a disc undergoes a standing-wave, bending vibration having nodes atthe concentric circles around the center of the glass plat shaped like adisc. This vibration removes the dust from the glass disc. The vibration(vibrational mode 1) produced by the voltage of the prescribed frequencyis a standing wave having nodes at the concentric circles around thecenter of the disc. The dust particles at these nodes cannot be removed,because the amplitude of vibration at the nodes is small. In view ofthis, the glass plat shaped like a disc is vibrated at a differentfrequency, achieving a standing-wave vibration (vibrational mode 2) thathas nodes at concentric circles different from those at which the nodesof vibrational mode 1 are located. Thus, those parts of the glass disc,where the nodes lie in vibrational mode 1, are vibrated at largeamplitude.

Jpn. Pat. Appln. KOKAI Publication No. 2007-228246 discloses arectangular dust-screening member and piezoelectric elements secured tothe opposite sides of the dust-screening member, respectively. Thepiezoelectric elements produce vibration at a predetermined frequency,resonating the dust-screening member. Vibration is thereby achieved insuch mode that nodes extend parallel to the sides of the dust-screeningmember. Further, as in the mechanism of U.S. 2004/0169761 A1, thedust-screening member is made to resonate at a different frequency,accomplishing a standing-wave vibrational mode, in order to change theopposition of nodes. Any one of these vibrational modes achieves bendingvibration having nodes extending parallel to the sides of thedust-screening member.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda vibrating device comprising: a vibrating device comprising:

a vibrator including: a dust-screening member which is shaped like aplate as a whole and has at least one side that is symmetric withrespect to a symmetry axis; and a vibrating member secured to thedust-screening member and configured to produce, at the dust-screeningmember, vibration having a vibrational amplitude perpendicular to asurface of the dust-screening member; and

a hold and support member configured to hold and support the vibrator toa fixed member, wherein

the hold and support position by the hold and support member is arrangedat position along a circle or ellipse concentric to the centroid of thevibrator such that peak ridges of the vibration having a vibrationalamplitude perpendicular to the surface of the dust-screening member formclosed loops.

According to a second aspect of the present invention, there is providedan image equipment comprising: an image equipment comprising:

an image forming element having an image surface on which an opticalimage is formed;

a vibrator including: a dust-screening member which is shaped like aplate as a whole, has at least one side that is symmetric with respectto a symmetry axis, and has a light-transmitting region at leastspreading to a predetermined region, facing the image surface and spacedtherefrom by a predetermined distance; and a vibrating member configuredto produce vibration having an amplitude perpendicular to a surface ofthe dust-screening member, the vibrating member being provided on thedust-screening member, outside the light-transmitting region throughwhich a light beam forming an optical image on the image surface passes;

a sealing structure for surrounding the image forming element and thedust-screening member, thereby providing a closed space in which theimage forming element and the dust-screening member that face eachother; and

a hold and support member configured to hold and support the vibrator tothe sealing structure, wherein

the hold and support position by the hold and support member is arrangedat position along a circle or ellipse concentric to the centroid of thevibrator such that peak ridges of the vibration having a vibrationalamplitude perpendicular to the surface of the dust-screening member formclosed loops.

Advantages of the invention will be set forth in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the invention. Advantages of the invention may berealized and obtained by means of the instrumentalities and combinationsparticularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram schematically showing an exemplary systemconfiguration, mainly electrical, of a lens-exchangeable, single-lensreflex electronic camera (digital camera) that is a first embodiment ofthe image equipment according to this invention;

FIG. 2A is a vertical side view of an image sensor element unit of thedigital camera, which includes a dust removal mechanism (or a sectionalview taken along line A-A shown in FIG. 2B);

FIG. 2B is a front view of the dust removal mechanism, as viewed fromthe lens side;

FIG. 3 is an exploded perspective view showing a major component(vibrator) of the dust removal mechanism;

FIG. 4A is a front view of a dust filter, explaining how the dust filteris vibrated;

FIG. 4B is a sectional view of the dust filter, taken along line B-Bshown in FIG. 4A;

FIG. 4C is a sectional view of the dust filter, taken along line C-Cshown in FIG. 4A;

FIG. 5 is a diagram explaining the length of the sides of the dustfilter orthogonal to the sides at which the piezoelectric elements arearranged, and the length of the piezoelectric element arranged sides;

FIG. 6A is a diagram explaining the concept of vibrating the dustfilter;

FIG. 6B is a front view of the dust filter vibrated in such a mode thatnode areas, where vibration hardly occurs, form a lattice pattern;

FIG. 7 is a graph showing the relation the vibration speed ratio and theaspect ratio have if the cushion members (hold and support member) arearranged and held on a circle concentric to the center of the vibratorhaving piezoelectric elements arranged on the dust filter of FIG. 4A.The graph also shows the relation the vibration speed ratio and theaspect ratio have if the dust filter is made to undergo free vibration;

FIG. 8 is a diagram explaining how the dust filter is vibrated inanother mode;

FIG. 9 is a diagram explaining how the dust filter is vibrated in stillanother mode;

FIG. 10 is a diagram showing the relation between the aspect ratio ofthe dust filter shown in FIG. 4A and the vibration speed ratio of thecenter part of the dust filter;

FIG. 11 is a diagram showing the relation between the length ratio ofthe piezoelectric elements arranged on the dust filter of FIGS. 4A to 4Cand the vibration speed ratio of the center part of the dust filter;

FIG. 12 is a diagram showing another configuration the dust filter mayhave;

FIG. 13 is a diagram showing still another configuration the dust filtermay have;

FIG. 14 is a conceptual diagram of the dust filter, explaining thestanding wave that is produced in the dust filter;

FIG. 15A is a diagram showing an electric equivalent circuit that drivesthe vibrator at a frequency near the resonance frequency;

FIG. 15B is a diagram showing an electric equivalent circuit that drivesthe vibrator at the resonance frequency;

FIG. 16 is a circuit diagram schematically showing the configuration ofa dust filter control circuit;

FIG. 17 is a timing chart showing the signals output from the componentsof the dust filter control circuit;

FIG. 18A is the first part of a flowchart showing an exemplary camerasequence (main routine) performed by the microcomputer for controllingthe digital camera body according to the first embodiment;

FIG. 18B is the second part of the flowchart showing the exemplarycamera sequence (main routine);

FIG. 19 is a flowchart showing the operating sequence of “silentvibration” that is a subroutine shown in FIG. 18A;

FIG. 20 is a flowchart showing the operation sequence of the “displayprocess” performed at the same time Step S201 of “silent vibration,”i.e. subroutine (FIG. 19), is performed;

FIG. 21 is a flowchart showing the operating sequence of the “displayprocess” performed at the same time Step S203 of “silent vibration,”i.e., or subroutine (FIG. 19), is performed;

FIG. 22 is a flowchart showing the operating sequence of the “displayprocess” performed at the same time Step S205 of “silent vibration,”i.e., subroutine (FIG. 19), is performed;

FIG. 23 is a diagram showing the form of a resonance-frequency wavecontinuously supplied to vibrating members during silent vibration; and

FIG. 24 is a flowchart showing the operating sequence of “silentvibration,” i.e., subroutine in the operating sequence of the digitalcamera that is a second embodiment of the image equipment according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Best modes of practicing this invention will be described with referenceto the accompanying drawings.

First Embodiment

An image equipment according to this invention, which will beexemplified below in detail, has a dust removal mechanism for the imagesensor element unit that performs photoelectric conversion to produce animage signal. Here, a technique of improving the dust removal functionof, for example, an electronic camera (hereinafter called “camera” willbe explained. The first embodiment will be described, particularly inconnection with a lens-exchangeable, single-lens reflex electroniccamera (digital camera), with reference to FIGS. 1 to 2B.

First, the system configuration of a digital camera 10 according to thisembodiment will be described with reference to FIG. 1. The digitalcamera 10 has a system configuration that comprises body unit 100 usedas camera body, and a lens unit 200 used as an exchange lens, i.e., oneof accessory devices.

The lens unit 200 can be attached to and detached from the body unit 100via a lens mount (not shown) provided on the front of the body unit 100.The control of the lens unit 200 is performed by the lens-controlmicrocomputer (hereinafter called “Lucom”) 201 provided in the lens unit200. The control of the body unit 100 is performed by the body-controlmicrocomputer (hereinafter called “Bucom” 101 provided in the body unit100. By a communication connector 102, the Lucom 210 and the Bucom 101are electrically connected to each other, communicating with each other,while the lens unit 200 remains attached to the body unit 100. The Lucom201 is configured to cooperate, as subordinate unit, with the Bucom 101.

The lens unit 200 further has a photographic lens 202, a diaphragm 203,a lens drive mechanism 204, and a diaphragm drive mechanism 205. Thephotographic lens 202 is driven by a DC motor (not shown) that isprovided in the lens drive mechanism 204. The diaphragm 203 is driven bya stepping motor (not shown) that is provided in the diaphragm drivemechanism 205. The Lucom 201 controls these motors in accordance withthe instructions made by the Bucom 101.

In the body unit 100, a penta-prism 103, a screen 104, a quick returnmirror 105, an ocular lens 106, a sub-mirror 107, a shutter 108, an AFsensor unit 109, an AF sensor drive circuit 110, a mirror drivemechanism 111, a shutter cocking mechanism 112, a shutter controlcircuit 113, a photometry sensor 114, and a photometry circuit 115 arearranged as shown in FIG. 1. The penta-prism 103, the screen 104, thequick return mirror 105, the ocular lens 106, and the sub-mirror 107 aresingle-lens reflex components that constitute an optical system. Theshutter 108 is a focal plane shutter arranged on the photographicoptical axis. The AF sensor unit 109 receives a light beam reflected bythe sub-mirror 107 and detects the degree of defocusing.

The AF sensor drive circuit 110 controls and drives the AF sensor unit109. The mirror drive mechanism 111 controls and drives the quick returnmirror 105. The shutter cocking mechanism 112 biases the spring (notshown) that drives the front curtain and rear curtain of the shutter108. The shutter control circuit 113 controls the motions of the frontcurtain and rear curtain of the shutter 108. The photometry sensor 114detects the light beam coming from the penta-prism 103. The photometrycircuit 115 performs a photometry process on the basis of the light beamdetected by the photometry sensor 114.

In the body unit 100, an image acquisition unit 116 is further providedto perform photoelectric conversion on the image of an object, which haspassed through the above-mentioned optical system. The image acquisitionunit 116 is a unit composed of a CCD 117 that is an image sensor elementas an image forming element, an optical low-pass filter (LPF) 118 thatis arranged in front of the CCD 117, and a dust filter 119 that is adust-screening member. Thus, in this embodiment, a transparent glassplate (optical element) that has, at least at its transparent part, arefractive index different from that of air is used as the dust filter119. Nonetheless, the dust filter 119 is not limited to a glass plate(optical element). Any other member (optical element) that exists in theoptical path and can transmit light may be used instead. For example,the transparent glass plate (optical element) may be replaced by anoptical low-pass filter (LPF), an infrared-beam filter, a deflectionfilter, a half mirror, or the like. In this case, the frequency anddrive time pertaining to vibration and the position of a vibrationmember (later described) are set in accordance with the member (opticalelement). The CCD 117 is used as an image sensor element. Nonetheless,any other image sensor element, such as CMOS or the like, may be usedinstead.

As mentioned above, the dust filter 119 can be selected from variousdevices including an optical low-pass filter (LPF). However, thisembodiment will be described on the assumption that the dust filter is aglass plate (optical element).

To the circumferential edge of the dust filter 119, two piezoelectricelements 120 a and 120 b are attached. The piezoelectric elements 120 aand 120 b have two electrodes each. A dust filter control circuit 121,which is a drive unit, drives the piezoelectric elements 120 a and 120 bat the frequency determined by the size and material of the dust filter119. As the piezoelectric elements 120 a and 120 b vibrate, the dustfilter 119 undergoes specific vibration. Dust can thereby be removedfrom the surface of the dust filter 119. To the image acquisition unit116, an anti-vibration unit is attached to compensate for the motion ofthe hand holding the digital camera 10.

The digital camera 10 according to this embodiment further has a CCDinterface circuit 122, a liquid crystal monitor 123, an SDRAM 124, aFlash ROM 125, and an image process controller 126, thereby to performnot only an electronic image acquisition function, but also anelectronic record/display function. The CCD interface circuit 122 isconnected to the CCD 117. The SDRAM 124 and the Flash ROM 125 functionas storage areas. The image process controller 126 uses the SDRAM 124and the Flash ROM 125, to process image data. A recording medium 127 isremovably connected by a communication connector (not shown) to the bodyunit 100 and can therefore communicate with the body unit 100. Therecording medium 127 is an external recording medium, such as one ofvarious memory cards or an external HDD, and records the image dataacquired by photography. As another storage area, a nonvolatile memory128, e.g., EEPROM, is provided and can be accessed from the Bucom 101.The nonvolatile memory 128 stores prescribed control parameters that arenecessary for the camera control.

To the Bucom 101, there are connected an operation display LCD 129, anoperation display LED 130, a camera operation switch 131, and a flashcontrol circuit 132. The operation display LCD 129 and the operationdisplay LED 130 display the operation state of the digital camera 10,informing the user of this operation state. The operation display LED129 or the operation display LED 130 has, for example, a display unitconfigured to display the vibration state of the dust filter 119 as longas the dust filter control circuit 121 keeps operating. The cameraoperation switch 131 is a group of switches including, for example, arelease switch, a mode changing switch, a power switch, which arenecessary for the user to operate the digital camera 10. The flashcontrol circuit 132 drives a flash tube 133.

In the body unit 100, a battery 134 used as power supply and apower-supply circuit 135 are further provided. The power-supply circuit135 converts the voltage of the battery 134 to a voltage required ineach circuit unit of the digital camera 10 and supplies the convertedvoltage to the each circuit unit. In the body unit 100, too, a voltagedetecting circuit (not shown) is provided, which detects a voltagechange at the time when a current is supplied from an external powersupply though a jack (not shown).

The components of the digital camera 10 configured as described aboveoperate as will be explained below. The image process controller 126controls the CCD interface circuit 122 in accordance with theinstructions coming from the Bucom 101, whereby image data is acquiredfrom the CCD 117. The image data is converted to a video signal by theimage process controller 126. The image represented by the video signalis displayed by the liquid crystal monitor 123. Viewing the imagedisplayed on the liquid crystal monitor 123, the user can confirm theimage photographed.

The SDRAM 124 is a memory for temporarily store the image data and isused as a work area in the process of converting the image data. Theimage data is held in the recording medium 127, for example, after ithas been converted to JPEG data.

The mirror drive mechanism 111 is a mechanism that drives the quickreturn mirror 105 between an up position and a down position. While thequick return mirror 105 stays at the down position, the light beamcoming from the photographic lens 202 is split into two beams. One beamis guide to the AF sensor unit 109, and the other beam is guided to thepenta-prism 103. The output from the AF sensor provided in the AF sensorunit 109 is transmitted via the AF sensor drive circuit 110 to the Bucom101. The Bucom 101 performs the distance measuring of the known type. Inthe meantime, a part of the light beam, which has passed through thepenta-prism 103, is guided to the photometry sensor 114 that isconnected to the photometry circuit 115. The photometry circuit 115performs photometry of the known type, on the basis of the amount oflight detected by the photometry sensor 114.

The image acquisition unit 116 that includes the CCD 117 will bedescribed with reference to FIGS. 2A and 2B. Note that the hatched partsshown in FIG. 2B show the shapes of members clearly, not to illustratingthe sections thereof.

As described above, the image acquisition unit 116 has the CCD 117, theoptical LPF 118, the dust filter 119, and the piezoelectric elements 120a and 120 b. The CCD 117 is an image sensor element that produces animage signal that corresponds to the light applied to its photoelectricconversion surface through the photographic optical system. The opticalLPF 118 is arranged at the photoelectric conversion surface of the CCD117 and removes high-frequency components from the light beam comingfrom the object through the photographic optical system. The dust filter119 is a dust-screening member arranged in front of the optical LPF 118and facing the optical LPF 118, spaced apart therefrom by apredetermined distance. The piezoelectric elements 120 a and 120 b arearranged on the circumferential edge of the dust filter 119 and arevibrating members for applying specific vibration to the dust filter119.

The CCD chip 136 of the CCD 117 is mounted directly on a flexiblesubstrate 137 that is arranged on a fixed plate 138. From the ends ofthe flexible substrate 137, connection parts 139 a and 139 b extend.Connectors 140 a and 140 b are provided on a main circuit board 141. Theconnection parts 139 a and 139 b are connected to the connectors 140 aand 140 b, whereby the flexible substrate 137 is connected to the maincircuit board 141. The CCD 117 has a protection glass plate 142. Theprotection glass plate 142 is secured to the flexible substrate 137,with a spacer 143 interposed between it and the flexible substrate 137.

Between the CCD 117 and the optical LPF 118, a filter holding member 144made of elastic material is arranged on the front circumferential edgeof the CCD 117, at a position where it does not cover the effective areaof the photoelectric conversion surface of the CCD 117. The filterholding member 144 abuts on the optical LPF 118, at a part close to therear circumferential edge of the optical LPF 118. The filter holdingmember 144 functions as a sealing member that maintains the junctionbetween the CCD 117 and the optical LPF 118 almost airtight. A holder145 is provided, covering seals the CCD 117 and the optical LPF 118 inairtight fashion. The holder 145 has a rectangular opening 146 in a partthat is substantially central around the photographic optical axis. Theinner circumferential edge of the opening 146, which faces the dustfilter 119, has a stepped part 147 having an L-shaped cross section.Into the opening 146, the optical LPF 118 and the CCD 117 are fittedfrom the back. In this case, the front circumferential edge of theoptical LPF 118 contacts the stepped part 147 in a virtually airtightfashion. Thus, the optical LPF 118 is held by the stepped part 147 at aspecific position in the direction of the photographic optical axis. Theoptical LPF 118 is therefore prevented from slipping forwards from theholder 145. The level of airtight sealing between the CCD 117 and theoptical LPF 118 is sufficient to prevent dust from entering to form animage having shadows of dust particles. In other words, the sealinglevel need not be so high as to completely prevent the in-flow ofgasses.

On the front circumferential edge of the holder 145, a dust-filterholding unit 148 is provided, covering the entire front circumferentialedge of the holder 145. The dust-filter holding unit 148 is formed,surrounding the stepped part 147 and projecting forwards from thestepped part 147, in order to hold the dust filter 119 in front of theLPF 118 and to space the filter 119 from the stepped part 147 by apredetermined distance. The opening of the dust-filter holding unit 148serves as focusing-beam passing area 149. The dust filter 119 is shapedlike a polygonal plate as a whole (a square plate, in this embodiment).The dust filter 119 is supported on the dust-filter holding unit 148,pushed onto the dust-filter holding unit 148 by a pushing member 150which is constituted by an elastic body such as a leaf spring and hasone end fastened with screws 151 to the dust-filter holding unit 148.More specifically, a cushion member 152 made of vibration attenuatingmaterial, such as rubber or resin, is interposed between the pushingmember 150 and the dust filter 119. On the other hand, between the backof the dust filter 119 and the dust-filter holding unit 148, a cushionmember 153 is interposed, which is almost symmetric with respect to thephotographic optical axis and which is made of vibration-attenuatingmaterial such as rubber. The cushion members 152 and 153 hold andsupport the dust filter 119 so that the vibration of the dust filter 119will not be transmitted to the pushing member 150 or the holder 145. Inthis embodiment, the cushion members 152 and 153 are arranged along acircle 154 concentric to the center O of a vibrator 155 composed of thedust filter 119 and the piezoelectric elements 120 a and 120 b, as isillustrated in FIG. 2B. More specifically, the cushion members 152 and153 are arranged with their centerlines extending in the lengthwisedirection and almost aligned with the concentric circle 154, as shown inFIG. 2B. Alternatively, the cushion members 152 and 153 may be arrangedwith their centerline extending along the concentric circle 154. In thismanner, the cushion members 152 and 153 function as hold and supportmember that hold and support the vibrator 155 relative to the pushingmember 150 and holder 145 that serve as holding members, and nodes areforcibly provided at positions corresponding to the cushion members 152and 153. Even if the dust filter is not circular, it can be regarded asa pseudo-circular dust filter defined by the concentric circles 154.This structure is advantageous in that the vibrational amplitudeincreases in inverse proportion to the distance to the centroid, and thevibrational amplitude is as great as possible and resembles that of acircular dust filter. The dust filter 119 is positioned with respect tothe Y-direction in the plane that is perpendicular to the optical axis,as that part of the pushing member 150 which is bent in the Z-direction,receive a force through a support member 156. On the other hand, thedust filter 119 is positioned with respect to the X-direction in theplane that is perpendicular to the optical axis, as a support part 157provided on the holder 145 receive a force through the support member156, as is illustrated in FIG. 2B. The support member 156 is locatedinward of a circle that surrounds the centroid of the vibrator 155. Thesupport member 156 is made of vibration-attenuating material such asrubber or resin, too, not to impede the vibration of the dust filter119. The cushion members 152 and 153 may be located at nodes of thevibration of the dust filter 119, which will be described later. In thiscase, the vibration of the dust filter 119 will be almost impeded. Thiscan provide an efficient dust removal mechanism that achieves vibrationof large amplitude. Between the circumferential edge of the dust filter119 and the dust-filter holding unit 148, a seal 158 having an annularlip part is arranged, defining an airtight space including an opening146. The image acquisition unit 116 is thus configured as an airtightstructure that has the holder 145 having a desired size and holding theCCD 117. The level of airtight sealing between the dust filter 119 andthe dust-filter holding unit 148 is sufficient to prevent dust fromentering to form an image having shadows of dust particles. The sealinglevel need not be so high as to completely prevent the in-flow ofgasses.

As described above, the dust filter 119 is supported to the dust-filterholding unit 148 by the pushing member 150 via the cushion members 152and 153. Nonetheless, the dust filter 119 may be supported by the seal158, not by the cushion member 153 at least.

To the ends of the piezoelectric elements 120 a and 120 b, which arevibrating members, flexes 159 a and 159 b, i.e., flexible printedboards, are electrically connected. The flexes 159 a and 159 b input anelectric signal (later described) from the dust filter control circuit121 to the piezoelectric elements 120 a and 120 b, causing the elements120 a and 120 b to vibrate in a specific way. The flexes 159 a and 159 bare made of resin and cupper etc., and have flexibility. Therefore, theylittle attenuate the vibration of the piezoelectric elements 120 a and120 b. The flexes 159 a and 159 b are provided at positions where thevibrational amplitude is small (at the nodes of vibration, which will bedescribed later), and can therefore suppress the attenuation ofvibration. The piezoelectric elements 120 a and 120 b move relative tothe body unit 100 if the camera 10 has such a hand-motion compensatingmechanism as will be later described. Hence, if the dust filter controlcircuit 121 is held by a holding member formed integral with the bodyunit 100, the flexes 159 a and 159 b are deformed and displaced as thehand-motion compensating mechanism operates. In this case, the flexes159 a and 159 b effectively work because they are thin and flexible. Inthe present embodiment, the flexes 159 a and 159 b have a simpleconfiguration, extending from two positions. They are best fit for usein cameras having a hand-motion compensating mechanism.

The dust removed from the surface of the dust filter 119 falls onto thebottom of the body unit 100, by virtue of the vibration inertia and thegravity. In this embodiment, a base 160 is arranged right below the dustfilter 119, and a holding member 161 made of, for example, adhesivetape, is provided on the base 160. The holding member 161 reliably trapsthe dust fallen from the dust filter 119, preventing the dust frommoving back to the surface of the dust filter 119.

The hand-motion compensating mechanism will be explained in brief. Asshown in FIG. 1, the hand-motion compensating mechanism is composed ofan X-axis gyro 162, a Y-axis gyro 163, a vibration control circuit 164,an X-axis actuator 165, a Y-axis actuator 166, an X-frame 167, a Y-frame168 (holder 145), a frame 169, a position sensor 170, and an actuatordrive circuit 171. The X-axis gyro 162 detects the angular velocity ofthe camera when the camera moves, rotating around the X axis. The Y-axisgyro 163 detects the angular velocity of the camera when the camerarotates around the Y axis. The vibration control circuit 164 calculatesa value by which to compensate the hand motion, from theangular-velocity signals output from the X-axis gyro 162 and Y-axis gyro163. In accordance with the hand-motion compensating value thuscalculated, the actuator drive circuit 171 moves the CCD 117 in theX-axis direction and Y-axis direction, which are first and seconddirections orthogonal to each other in the XY plane that isperpendicular to the photographic optical axis, thereby to compensatethe hand motion, if the photographic optical axis is taken as Z axis.More precisely, the X-axis actuator 165 drives the X-frame 167 in theX-axis direction upon receiving a drive signal from the actuator drivecircuit 171, and the Y-axis actuator 166 drives the Y-frame 168 in theY-axis direction upon receiving a drive signal from the actuator drivecircuit 171. That is, the X-axis actuator 165 and the Y-axis actuator166 are used as drive sources, the X-frame 167 and the Y-frame 168(holder 145) which holds the CCD 117 of the image acquisition unit 116are used as objects that are moved with respect to the frame 169. Notethat the X-axis actuator 165 and the Y-axis actuator 166 are eachcomposed of an electromagnetic motor, a feed screw mechanism, and thelike. Alternatively, each actuator may be a linear motor using a voicecoil motor, a linear piezoelectric motor or the like. The positionsensor 170 detects the position of the X-frame 167 and the position ofthe Y-frame 168. On the basis of the positions the position sensor 170have detected, the vibration control circuit 164 controls the actuatordrive circuit 171, which drives the X-axis actuator 165 and the Y-axisactuator 166. The position of the CCD 117 is thereby controlled.

The dust removal mechanism of the first embodiment will be described indetail, with reference to FIGS. 3 to 14. The dust filter 119 has atleast one side symmetric with respect to a certain symmetry axis, and isa glass plate (optical element) of a polygonal plate as a whole (asquare plate, in this embodiment). The dust filter 119 has a regionflaring in the radial direction from the position at which maximumvibrational amplitude is produced. This region forms a transparent part.Alternatively, the dust filter 119 may be D-shaped, formed by cutting apart of a circular plate, thus defining one side. Still alternatively,it may formed by cutting a square plate, having two opposite sidesaccurately cut and having upper and lower sides. The above-mentionedfastening mechanism fastens the dust filter 119, with the transparentpart opposed to the front of the LPF 118 and spaced from the LPF 118 bya predetermined distance. To one surface of the dust filter 119 (i.e.,back of the filter 119, in this embodiment), the piezoelectric elements120 a and 120 b, which are vibrating members, are secured at the upperand lower edges of the filter 119, by means of adhesion using adhesive.The piezoelectric elements 120 a and 120 b, which are arranged on thedust filter 119, constitute a vibrator 155. The vibrator 155 undergoesresonance when a voltage of a prescribed frequency is applied to thepiezoelectric elements 120 a and 120 b. The resonance achieves suchbending vibration of a large amplitude, as illustrated in FIGS. 4A to4C.

As shown in FIG. 3, signal electrodes 173 a and 174 a are formed on thepiezoelectric element 120 a, and signal electrodes 173 b and 174 b areformed on the piezoelectric element 120 b. Note that the hatched partsshown in FIG. 3 show the shapes of the signal electrodes clearly, not toillustrating the sections thereof. The signal electrodes 174 a and 174 bare provided on the back opposing the signal electrodes 173 a and 173 b,and are bent toward that surface of the piezoelectric element 120 a, onwhich the signal electrodes 173 a and 173 b are provided. The flex 159 ahaving the above-mentioned conductive pattern is electrically connectedto the signal electrode 173 a and signal electrode 174 a. The flex 159 bhaving the above-mentioned conductive pattern is electrically connectedto the signal electrode 173 b and signal electrode 174 b. To the signalelectrodes 173 a, 173 b, 174 a and 174 b, a drive voltage of theprescribed frequency is applied form the dust filter control circuit 121through flexes 159 a and 159 b. The drive voltage, thus applied, cancause the dust filter 119 to undergo such a two-dimensional,standing-wave bending vibration as is shown in FIGS. 4A to 4C. Thosesides of the dust filter 119, at which the piezoelectric elements 120 aand 120 b are arranged, have length LA. The piezoelectric elements 120 aand 120 b have length LP. (This size notation accords with the sizenotation used in FIG. 5.) Since the dust filter 119 shown in FIG. 4A isrectangular, it is identical in shape to the “virtual rectangle”according to this invention (later described). Hence, the sides LA ofthe dust filter 119, at which the piezoelectric elements 120 a and 120 bare arranged, are identical to the sides LF of the virtual rectanglethat include the sides LA. The bending vibration shown in FIG. 4A isstanding wave vibration. In FIG. 4A, the blacker the streaks, eachindicating a node area 175 of vibration (i.e., area where thevibrational amplitude is small), the smaller the vibrational amplitudeis. Note that the meshes shown in FIG. 4A are division meshes usuallyused in the final element method.

If the node areas 175 are at short intervals as shown in FIG. 4A whenthe vibration speed is high, in-plane vibration (vibration along thesurface) will occur in the node areas 175. This vibration induces alarge inertial force in the direction of the in-plane vibration (seemass point Y2 in FIG. 14, described later, which moves over the nodealong an arc around the node, between positions Y2 and Y2′) to the dustat the node areas 175. If the dust filter 119 is inclined to becomeparallel to the gravity so that a force may act along the dust receivingsurface, the inertial force and the gravity can remove the dust from thenode areas 175.

In FIG. 4A, the white areas indicate areas where the vibrationalamplitude is large. The dust adhering to any white area is removed bythe inertial force exerted by the vibration. The dust can be removedfrom the node areas 175, too, by producing vibration in another mode, atsimilar amplitude at each node area 175.

The bending vibrational mode shown in FIG. 4A is achieved bysynthesizing the bending vibration of the X-direction and the bendingvibration of the Y-direction. The fundamental state of this synthesis isshown in FIG. 6A. If the cushion members 152 and 153 are not arranged onthe concentric circle 154, not holding or supporting the vibrator 155,and if the vibrator 155 is mounted on a member that only slightlyattenuates the vibration, such as a foamed rubber block, and is vibratedfreely, a vibrational mode in which such lattice-shaped node areas 173as shown in FIG. 6B are produced can be easily attained (see Jpn. Pat.Appln. KOKAI Publication No. 2007-228246, identified above). In thefront view included in FIG. 6A, the broken lines define the node areas175 shown in FIG. 6B (more precisely, the lines indicate the positionswhere the vibrational amplitude is minimal in the widthwise direction oflines). In this case, a standing wave, bending vibration at wavelengthλ_(x) occurs in the X-direction, and a standing wave, bending vibrationat wavelength λ_(y) occurs in the Y-direction. These standing waves aresynthesized as shown in FIG. 6B. With respect to the origin (x=0, y=0),the vibration Z (x, y) at a given point P (x, y) is expressed byEquation 1, as follows:

Z(x,y)=A·W _(mn)(x,y)·cos(γ)+A·W _(nm)(x,y)·sin(γ)  (1)

where A is amplitude (a fixed value here, but actually changing with thevibrational mode or the power supplied to the piezoelectric elements); mand n are positive integers including 0, indicating the order of naturalvibration corresponding to the vibrational mode; γ is a given phaseangle;

${{W_{mn}( {x,y} )} = {{\sin ( {{n\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{m\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};{and}$${W_{nm}( {x,y} )} = {{\sin ( {{m\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {{\sin ( {{n\; {\pi \cdot y}} + \frac{\pi}{2}} )}.}}$

Assume that the phase angle γ is 0 (γ=0). Then, Equation 1 changes to:

$\begin{matrix}{{Z( {x,y} )} = {A \cdot {W_{mn}( {x,y} )}}} \\{= {A \cdot {\sin ( {\frac{n \cdot \pi \cdot x}{\lambda_{x}} + \frac{\pi}{2}} )} \cdot {{\sin ( {\frac{m \cdot \pi \cdot y}{\lambda_{y}} + \frac{\pi}{2}} )}.}}}\end{matrix}$

Further assume that λ_(x)=λ_(y)=λ=1 (x and y are represented by the unitof the wavelength of bending vibration). Then:

$\begin{matrix}{{Z( {x,y} )} = {A \cdot {W_{mn}( {x,y} )}}} \\{= {A \cdot {\sin ( {{n \cdot \pi \cdot x} + \frac{\pi}{2}} )} \cdot {{\sin ( {{m \cdot \pi \cdot y} + \frac{\pi}{2}} )}.}}}\end{matrix}$

FIG. 6B shows the vibrational mode that is applied if m=n (since theX-direction vibration and the Y-direction vibration are identical interms of order and wavelength, the dust filter 119 has a square shape).In this vibrational mode, the peaks, nodes and valleys of vibrationappear at regular intervals in both the X-direction and the Y-direction,and vibration node areas 175 appear as a checkerboard pattern(conventional vibrational mode). In the vibrational mode where m=0, n=1,the vibration has peaks, nodes and valleys parallel to a side thatextends parallel to the Y-direction. In the vibrational mode identifiedwith a checkerboard pattern or peaks, nodes and valleys parallel to aside, the X-direction vibration and the Y-direction vibration remainindependent, never synthesized to increase the vibrational amplitude.

In view of this, the dust filter 119 may be elongated a little, shapedlike a rectangle, and may be vibrated at a specific frequency, or in amode where m=3 and n=2. In this vibrational mode, the phase angle γ is+Π/4 or ranges from −Π/4 to −Π/8. This vibrational mode is a mode inwhich the present embodiment will have very large vibrational amplitude(the maximum amplitude is at the same level as at the conventionalcircular dust filter). If γ=+Π/4, the vibrational mode will be the modeshown in FIG. 4A. In this vibrational mode, the peak ridges 176 ofvibrational amplitude form closed loops around the optical axis thoughthe dust filter 119 is rectangular. In this state, the vibration speedis at the same level as seen from FIG. 7, regardless of whether thevibrator 155 is held by the cushion members 152 and 153 and extendsalong the concentric circuit 154 or is made to vibrate freely. Thevibration speed is nearly equal to the value obtained in the case wherethe dust filter is shaped like a circle in which the rectangular dustfilter 119 is inscribed.

FIG. 8 shows a vibrational mode achieved in a vibrational mode where thephase angle γ ranges from −Π/4 to −Π/8. More precisely, the dust filter119 is not freely supported as shown in FIG. 6A. Rather, the dust filter119 is held and supported by the cushion members 152 and 153, with itssides extending along the concentric circle 154 as shown in FIG. 8. Inthis case, the aspect ratio of the dust filter 119 (i.e., ratio of thelength LB of the sides orthogonal to the sides at which thepiezoelectric elements are arranged and which have length LA to thelength LA of the piezoelectric elements arranged sides) is 1.12. In thiscase, the length ratio of either piezoelectric element (i.e., ratio ofthe length LP of the piezoelectric element to the length LF of the sideof the dust filter 119 to which the piezoelectric element is arranged inparallel) is 0.68. In the dust filter 119 as shown in FIG. 8, the aspectratio (LB/LA) will result in the lowest vibration speed. In thisembodiment, the dust filter 119 is held and supported with its sidesextending along the concentric circle 154, the vibration-speed ratio(i.e., ratio of maximum speed V_(max) to the speed of vibrationperpendicular to the plane of the center part of the dust filter)increases by about 20% (see FIG. 7).

FIG. 9 shows a vibrational mode, in which the phase angle γ is close to−Π/4 though the dust filter 119 has an aspect ratio of 1.06, exceeding1, because the dust filter 119 is held and supported with its sidesextending along the concentric circle 154. In this vibrational mode,peak ridges 176 of vibration are formed and surround the respectivemidpoints of the sides. If the vibrator 155 is not supported as in thisembodiment, the vibration in this mode will be similar to thefundamental vibration of FIG. 6A, as in the case shown in FIG. 8. If thecushion members 152 and 153 used as hold and support member hold andsupport the vibrator 155, at positions along the concentric circle 154as shown in FIG. 9, the vibrational mode of FIG. 9 will be attained. Asthe graph of FIG. 7 shows, the vibration speed ratio is larger, by about40%, than in the case where the dust filter 119 is freely vibrated.Thus, the dust filter has an optimal aspect ratio if supported as inthis embodiment. Note that the piezoelectric elements of the vibrator155 shown in FIG. 9 have a length ratio of 0.68.

The dust filter 119 of the vibrator 155, shown in FIG. 4A, is a glassplate (optical element) having a size of 30.8 mm (X-direction: LA,LF)×28.5 mm (Y-direction: LB)×0.65 mm (thickness). The dust filter 119is rectangular, having long sides LA (30.8 mm, extending in theX-direction) and short sides LB (28.5 mm, extending in the Y-direction).Therefore, the dust filter 119 is identical to the “virtual rectangle”according to this invention, which has the same area as the dust filter119. The sides LA of the dust filter 119 at which the piezoelectricelements 120 a, 120 b are arranged are thus identical to the sides LF ofthe virtual rectangle that includes the sides LA. The piezoelectricelements 120 a and 120 b are made of lead titanate-zirconate ceramic andhave a size of 21 mm (X-direction: LP)×3 mm (Y-direction)×0.8 mm(thickness). The piezoelectric elements 120 a and 120 b are adhered withepoxy-based adhesive to the dust filter 119, extending along the upperand lower sides of the filter 119, respectively. More specifically, thepiezoelectric elements 120 a and 120 b extend in the X-direction andarranged symmetric in the left-right direction, with respect to thecenterline of the dust filter 119, which extends in the Y-direction. Inthis embodiment, the dust filter 119 has an aspect ratio of 0.925 andthe piezoelectric elements have a length ratio of 0.682. In this case,the resonance frequency in the vibrational mode of FIG. 4A is in thevicinity of 91 kHz. At the center of the dust filter 119, a maximalvibration speed and vibrational amplitude can be attained if the dustfilter is shaped like a circle in which the rectangular dust filter 119is inscribed. The vibration-speed ratio, which is the ratio of maximumspeed V_(max) to the speed of vibration perpendicular to the plane ofthe center part of the dust filter 119, has such a value as shown inFIG. 7, FIG. 10 and FIG. 11, the maximum value of which is 1.000.

FIG. 12 shows a modification of the vibrator 155. The modified vibrator155 has a dust filter 119 that is D-shaped, formed by cutting a part ofa circle, thus defining one side. That is, the modified vibrator 155uses a D-shaped dust filter 119 that has a side symmetric with respectto the Y-axis. The piezoelectric element 120 a is arranged on thesurface of the dust filter 119, extending parallel to that side andpositioned symmetric with respect to the midpoint of the side (or to asymmetry axis extending in the Y direction). On the other hand, thepiezoelectric element 120 b is substantially inscribed in the outercircumference of the dust filter 119 and extends parallel to that sideof the dust filter 119. The dust filter 119 is held and supported bythree arc cushion members 152 and 153 as hold and support member, whichare arranged on a circle 154 concentric to the center of the filter 119(regarded as the centroid). Since the dust filter 119 is so shaped, thehold and support member can be well arranged on the concentric circle154. So shaped, the dust filter 119 is more symmetric with respect toits center (regarded as the centroid), and can more readily vibrate in astate desirable to the present embodiment. In addition, the dust filter119 can be smaller than the circular one. Furthermore, since thepiezoelectric elements 120 a and 120 b arranged parallel to the side,the asymmetry in terms vibration, resulting from the cutting, can bemade more symmetric by increasing the rigidity. This helps to render thevibration state more desirable. Note that the long side and short sideshown in FIG. 12 are the long and short sides of a virtual rectangle 177which has the same area as the dust filter 119, one side of whichextends along the above-mentioned one side of the dust filter 119, andthe opposite side of which extends along an outer side of thepiezoelectric element 120 b.

FIG. 13 shows another modification of the vibrator 155. This modifiedvibrator 155 has a dust filter 119 is formed by cutting a circular platealong two parallel lines, forming two parallel sides. That is, themodified vibrator 155 uses a dust filter 119 that has two sidessymmetric with respect to the symmetry axis extending in theY-direction. In this case, actuate piezoelectric elements 120 a and 120b are arranged not on the straight sides, but on the curved partsdefining a circle. In this case, the vibrator 115 is held and supportedby two arc cushion members 152 and 153 as hold and support member thatextend around the center of the dust filter 119 and on the concentriccircle 154. More precisely, the cushion members 152 and 153 support thepiezoelectric elements 120 a and 120 b, respectively. The piezoelectricelements 120 a and 120 b are efficiently arranged in this configuration.This helps to render the vibrator 155 smaller than otherwise. Note thatthe long side and shot side shown in FIG. 13 are the long and shortsides of a virtual rectangle 177 which has the same area as the dustfilter 119, two opposite sides of which extend along the opposite twosides of the dust filter 119, respectively. The piezoelectric elements120 a and 120 b are arranged at the short sides (having length LF). Thepiezoelectric elements 120 a and 120 b have length LP as measured alongthe short sides of the virtual rectangle 177.

As described above, the dust filter may have a “D” shape or an ovalshape (which is obtained by linearly cutting out a circular shape insuch a manner that the resultant shape has two symmetric parallel linearlines). The dust filter having a “D” shape or an oval shape can be heldand supported at positions corresponding to the arc cushion members 152and 153, and nodes are forcibly provided at these positions. As aresult, the dust filter can be regarded as a pseudo-circular dust filterdefined by concentric circles 154. Since the vibrational amplitude isgreat at the centroid of the D-shaped dust filter or the oval dustfilter, the vibrational amplitude as a whole is as great as possible andis like that of a circular dust filter.

A method of removing dust will be explained in detail, with reference toFIG. 14. FIG. 14 shows a cross section identical to that shown in FIG.4B. Assume that the piezoelectric elements 120 a and 120 b are polarizedin the direction of arrow 178 as shown in FIG. 14. If a voltage of aspecific frequency is applied to the piezoelectric elements 120 a and120 b at a certain time to, the vibrator 155 will be deformed asindicated by solid lines. At the mass point Y existing at given positiony in the surface of the vibrator 155, the vibration z in the Z-directionis expressed by Equation 2, as follows:

z=A·sin(γ)·cos(ωt)  (2)

where ω is the angular velocity of vibration, A is the amplitude ofvibration in the Z-direction, and Y=2 ny/λ (λ: wavelength of bendingvibration).

The Equation 2 represents the standing-wave vibration shown in FIG. 4A.Thus, if y=s·λ/2 (here, s is an integer), then Y=sΠ, and sin(Y)=0.Hence, a node 179, at which the amplitude of vibration in theZ-direction is zero irrespective of time, exists for every Π/2. This isstanding-wave vibration. The state indicated by broken lines in FIG. 14takes place if t=kΠ/ω (k is odd), where the vibration assumes a phaseopposite to the phase at time t₀.

Vibration z(Y₁) at point Y₁ on the dust filter 119 is located at anantinode 180 of standing wave, bending vibration. Hence, the vibrationin the Z-direction has amplitude A, as expressed in Equation 3, asfollows:

z(Y ₁)=A·cos(ωt)  (3)

If Equation 3 is differentiated with time, the vibration speed Vz(Y₁) atpoint Y₁ is expressed by Equation 4, below, because ω=2Πf, where f isthe frequency of vibration:

$\begin{matrix}{{{Vz}( Y_{1} )} = {\frac{( {z( Y_{1} )} )}{t} = {{- 2}\; \pi \; {f \cdot A \cdot {\sin ( {\omega \; t} )}}}}} & (4)\end{matrix}$

If Equation 4 is differentiated with time, vibration acceleration αz(Y₁)is expressed by Equation 5, as follows:

$\begin{matrix}{{\alpha \; {z( Y_{1} )}} = {\frac{( {{Vz}( Y_{1} )} )}{t} = {{- 4}\; \pi^{2}{f^{2} \cdot A \cdot {\cos ( {\omega \; t} )}}}}} & (5)\end{matrix}$

Therefore, the dust 181 adhering at point Y₁ receives the accelerationof Equation 5. The inertial force Fk the dust 181 receives at this timeis given by Equation 6, as follows:

Fk=αz(Y ₁)·M=−4π² f ² ·A·cos(ωt)·M  (6)

where M is the mass of the dust 181.

As can be seen from Equation 6, the inertial force Fk increases asfrequency f is raised, in proportion to the square of f. However, theinertial force cannot be increased if amplitude A is small, no matterhow much frequency f is raised. Generally, kinetic energy of vibrationcan be produced, but in a limited value, if the piezoelectric elements120 a and 120 b that produce the kinetic energy have the same size.Therefore, if the frequency is raise in the same vibrational mode,vibrational amplitude A will change in inverse proportion to the squareof frequency f. Even if the resonance frequency is raised to achieve ahigher-order resonance mode, the vibrational frequency will fall, notincreasing the vibration speed or the vibration acceleration. Rather, ifthe frequency is raised, ideal resonance will hardly be accomplished,and the loss of vibrational energy will increase, inevitably decreasingthe vibration acceleration. That is, the mode cannot attain largeamplitude if the vibration is produced in a resonance mode that useshigh frequency only. The dust removal efficiency will be much impaired.

Although the dust filter 119 is rectangular, the peak ridges 176 ofvibrational amplitude form closed loops around the optical axis in thevibrational mode of the embodiment, which is shown in FIG. 4A. In thevibrational mode of the embodiment, which is shown in FIG. 8 or 9, thepeak ridges 176 of vibrational amplitude form curves surrounding themidpoint of each side. The wave reflected from the side extending in theX-direction and the wave reflected from the side extending in theY-direction are efficiently synthesized, forming a standing wave.

The shape and size of the dust filter 119 and the shape and size of thepiezoelectric elements 120 a and 120 b greatly contribute to efficientgeneration of this synthesized standing wave.

As seen from FIG. 10, it is better to set the aspect ratio (LB/LA, i.e.,ratio of the length LB of the sides orthogonal to the sides at which thepiezoelectric elements 120 a and 120 b are arranged and which havelength LA) to a value smaller than 1, than to 1 (to make the dust filter119 square). If the aspect ratio is smaller than 1, the speed ofvibration at the center of the dust filter 119, in the Z-direction willbe higher (the vibration speed ratio is 0.7 or more), no matter how thepiezoelectric elements 120 a and 120 b are arranged. In FIG. 10, theratio (V/V_(max)) of the vibration speed V to the maximum vibrationspeed V_(max) possible in this region is plotted on the ordinate. At theaspect ratio of 0.9 or less, the vibration speed abruptly decreases.Therefore, the dust filter 119 preferably has an aspect ratio (LB/LA) of0.9 to 1, but less than 1. Further, if the piezoelectric elements 120 aand 120 b are arranged at the short sides of the dust filter 119,inevitably increasing the aspect ratio (LB/LA) of the dust filter 119 toa value greater than 1, the ratio of vibration speed at the center ofthe dust filter 119 will decrease with respect to the Z-direction. It istherefore advisable to arrange the piezoelectric elements 120 a and 120b at the long sides of the dust filter 119, not at the short sidesthereof. If the elements 120 a and 120 b are so arranged, the vibrationspeed ratio will increase to achieve a high dust removal ability.

Even if the piezoelectric elements 120 a and 120 b at the shot sides ofthe dust filter 119, however, the vibration speed ration cannot be largeas shown in FIG. 7 since the vibrator 155 is supported by the cushionmembers arranged on the concentric circle 154. For example, the dustfilter 119 of the vibrator 115, shown in FIG. 8, is a glass plate(optical element) that has a size of 30.8 mm (X-direction: LA, LF)×34.5mm (Y-direction: LB)×0.65 mm (thickness). The piezoelectric elements aremade of lead titanate-zirconate ceramic and have a size of 21 mm(X-direction: LP)×3 mm (Y-direction)×0.8 mm (thickness). They areadhered with an epoxy-based adhesive to the dust filter 119, extendingalong the upper and lower sides of the filter 119, respectively, andpositioned symmetric in the X-direction with respect to the centerlineof the dust filter. In this case, the resonance frequency in thevibrational mode of FIG. 8 is in the vicinity of 80 kHz, the aspectratio (LB/LA) of the dust filter 119 is 1.12, and the length ratio(LP/LF) of the piezoelectric elements is 0.68. Thus, the aspect ratio ofthe dust filter 119 is 1.12, exceeding 1. Consequently, if the filter isvibrated freely, the vibration speed will be too low to achieve avibration speed ratio large enough to remove dust. Nonetheless, thevibration speed ratio can be increased by about 20%, because thestructure of FIG. 8 holds and supports the dust filter 119.

The vibration speed at the center position of the dust filter 119, asmeasured in the Z-direction, provides the widest possible region whenthe length ratio LP/LF of the piezoelectric elements is set at a valueless than 1, not at 1. This is obvious from FIG. 11, in which the lengthratio LP/LF of the piezoelectric elements 120 a and 120 b is plottedagainst the abscissa (LF: the length of a virtual rectangle having aside on which the piezoelectric elements 120 a and 120 b are arranged;LP: the length of the piezoelectric elements 120 a and 120 b arranged inparallel to length LF), and the vibration speed ratio at the center ofthe filter is plotted against the ordinate. In FIG. 11, the ratio(V/V_(max)) of the vibration speed V to the maximum vibration speedV_(max) possible in this region is plotted on the ordinate. The maximumvalue of the length ratio of the piezoelectric elements is, ofcourse, 1. If the length ratio of the piezoelectric elements is 0.5 orless, the vibration speed ratio will be less than 0.8. This means thatthe speed is lower than the maximum value by 20% or more. Hence, it ispreferable for the length ratio of the piezoelectric elements to be 0.5or more, but less than 1, in order to increase the vibration speed atthe center of the dust filter 119, with respect to the Z-direction (to0.7 or more).

In vibration wherein the peak ridges 176 of vibrational amplitude formclosed loops around the optical axis or the peak ridges 176 form curvessurrounding the midpoint of each side, the dust filter 119 can undergovibration of amplitude a similar to that of concentric vibration thatmay occur if the dust filter 119 has a disc shape. In any vibrationalmode in which the amplitude is simply parallel to the side, thevibration acceleration is only 10% or more of the acceleration achievedin this embodiment.

In the vibration wherein the peak ridges 176 of vibrational amplitudeform closed loops or curves surrounding the midpoint of each side, thevibrational amplitude is the largest at the center of the vibrator 155and small at the closed loop or the curve at circumferential edges.Thus, the dust removal capability is maximal at the center of the image.If the center of the vibrator 155 is aligned with the optical axis, theshadow of dust 181 will not appear in the center part of the image,which has high image quality. This is an advantage.

In the vibration node areas 175, which exist in the focusing-beampassing area 149, the nodes 179 may be changed in position by changingthe drive frequencies of the piezoelectric elements 120 a and 120 b.Then, the elements 120 a and 120 b resonate in a different vibrationalmode, whereby the dust can be removed, of course.

A vibration state that is attained if the piezoelectric elements 120 aand 120 b are driven at a frequency near the resonance frequency will bedescribed with reference to FIGS. 15A and 15B. FIG. 15A shows anequivalent circuit that drives the piezoelectric elements 120 a and 120b at a frequency near the resonance frequency. In FIG. 15A, C₀ is theelectrostatic capacitance attained as long as the piezoelectric elements120 a and 120 b remain connected in parallel, and L, C and R are thevalues of a coil, capacitor and resistor that constitute an electriccircuit equivalent to the mechanical vibration of the vibrator 155.Naturally, these values change with the frequency.

When the frequency changes to resonance frequency f₀, L and C achieveresonance as is illustrated in FIG. 15B. As the frequency is graduallyraised toward the resonance frequency from the value at which noresonance takes place, the vibration phase of the vibrator 155 changeswith respect to the phase of vibration of the piezoelectric elements 120a and 120 b. When the resonance starts, the phase reaches Π/2. As thefrequency is further raised, the phase reaches n. If the frequency israised even further, the phase starts decreasing. When the frequencycomes out of the resonance region, the phase becomes equal to the phasewhere no resonance undergoes at low frequencies. In the actualsituation, however, the vibration state does not become ideal. The phasedoes not change to n in some cases. Nonetheless, the drive frequency canbe set to the resonance frequency.

A support areas 182 shown at the corners of FIG. 4A, FIG. 8 and FIG. 9extend along the circle 154 that is concentric to the center of the dustfilter 119. Those parts of the dust filter 119 which are aligned withthe support areas 182 are pushed in the Z-direction, through the cushionmembers 152 and 153 made of a vibration-attenuating material such asrubber. So held, the dust filter 119 scarcely transmits its vibration tothe cushion members 152 and 153. Even if the dust filter 119 is securedto the cushion members 152 and 153 by means of, for example, adhesion,the vibration of the dust filter 119 will not be impaired. The dustfilter 119 can therefore be reliably supported (see FIG. 7).

On the other hand, the seal 158 must be provided in the area havingvibrational amplitude, too. In the vibrational mode of the presentinvention, the peripheral vibrational amplitude is small. In view ofthis, the dust filter 119 is supported, at circumferential edge, by thelip-shaped part of the seal 158, thereby applying no large force in thedirection of bending vibrational amplitude. Therefore, the seal 158attenuates, but very little, the vibration whose amplitude is inherentlysmall. As shown in FIG. 4A, FIG. 8 and FIG. 9, as many seal-contactparts 183 as possible contact the node areas 175 in which thevibrational amplitude is small. This further reduces the attenuation ofvibration.

The prescribed frequency at which to vibrate the piezoelectric elements120 a and 120 b is determined by the shape, dimensions, material andsupported state of the dust filter 119, which is one component of thevibrator 155. In most cases, the temperature influences the elasticitycoefficient of the vibrator 155 and is one of the factors that changethe natural frequency of the vibrator 155. Therefore, it is desirable tomeasure the temperature of the vibrator 155 and to consider the changein the natural frequency of the vibrator 155, before the vibrator 155 isused. A temperature sensor (not shown) is therefore connected to atemperature measuring circuit (not shown), in the digital camera 10. Thevalue by which to correct the vibrational frequency of the vibrator 155in accordance with the temperature detected by the temperature sensor isstored in the nonvolatile memory 128. Then, the measured temperature andthe correction value are read into the Bucom 101. The Bucom 101calculates a drive frequency, which is used as drive frequency of thedust filter control circuit 121. Thus, vibration can be produced, whichis efficient with respect to temperature changes, as well.

The dust filter control circuit 121 of the digital camera 10 accordingto this invention will be described below, with reference to FIGS. 16and 17. The dust filter control circuit 121 has such a configuration asshown in FIG. 16. The components of the dust filter control circuit 121produce signals (Sig1 to Sig4) of such waveforms as shown in the timingchart of FIG. 17. These signals will control the dust filter 119, aswill be described below.

More specifically, as shown in FIG. 16, the dust filter control circuit121 comprises a N-scale counter 184, a half-frequency dividing circuit185, an inverter 186, a plurality of MOS transistors Q₀₀, Q₀₁ and Q₀₂, atransformer 187, and a resistor R₀₀.

The dust filter control circuit 121 is so configured that a signal(Sig4) of the prescribed frequency is produced at the secondary windingof the transformer 187 when MOS transistors Q₀₁ and Q₀₂ connected to theprimary winding of the transformer 187 are turned on and off. The signalof the prescribed frequency drives the piezoelectric elements 120 a and120 b, thereby causing the vibrator 155, to which the dust filter 119 issecured, to produce a resonance standing wave.

The Bucom 101 has two output ports P_PwCont and D_NCnt provided ascontrol ports, and a clock generator 188. The output ports P_PwCont andD_NCnt and the clock generator 188 cooperate to control the dust filtercontrol circuit 121 as follows. The clock generator 188 outputs a pulsesignal (basic clock signal) having a frequency much higher than thefrequency of the signal that will be supplied to the piezoelectricelements 120 a and 120 b. This output signal is signal Sig1 that has thewaveform shown in the timing chart of FIG. 17. The basic clock signal isinput to the N-scale counter 184.

The N-scale counter 184 counts the pulses of the pulse signal. Everytime the count reaches a prescribed value “N,” the N-scale counter 184produces a count-end pulse signal. Thus, the basic clock signal isfrequency-divided by N. The signal the N-scale counter 184 outputs issignal Sig2 that has the waveform shown in the timing chart of FIG. 17.

The pulse signal produced by means of frequency division does not have aduty ratio of 1:1. The pulse signal is supplied to the half-frequencydividing circuit 185. The half-frequency dividing circuit 185 changesthe duty ratio of the pulse signal to 1:1. The pulse signal, thuschanged in terms of duty ratio, corresponds to signal Sig3 that has thewaveform shown in the timing chart of FIG. 17.

While the pulse signal, thus changed in duty ratio, is high, MOStransistor Q₀₁ to which this signal has been input is turned on. In themeantime, the pulse signal is supplied via the inverter 186 to MOStransistor Q₀₂. Therefore, while the pulse signal (signal Sig3) is lowstate, MOS transistor Q₀₂ to which this signal has been input is turnedon. Thus, the transistors Q₀₁ and Q₀₂, both connected to the primarywinding of the transformer 187, are alternately turned on. As a result,a signal Sig4 of such frequency as shown in FIG. 17 is produced in thesecondary winding of the transformer 187.

The winding ratio of the transformer 187 is determined by the outputvoltage of the power-supply circuit 135 and the voltage needed to drivethe piezoelectric elements 120 a and 120 b. Note that the resistor R₀₀is provided to prevent an excessive current from flowing in thetransformer 187.

In order to drive the piezoelectric elements 120 a and 120 b, MOStransistor Q₀₀ must be on, and a voltage must be applied from thepower-supply circuit 135 to the center tap of the transformer 187. Inthis case, MOS transistor Q₀₀ is turned on or off via the output portP_PwCont of the Bucom 101. Value “N” can be set to the N-scale counter184 from the output port D_NCnt of the Bucom 101. Thus, the Bucom 101can change the drive frequency for the piezoelectric elements 120 a and120 b, by appropriately controlling value “N.”

The frequency can be calculated by using Equation 7, as follows:

$\begin{matrix}{{fdrv} = \frac{fpls}{2\; N}} & (7)\end{matrix}$

where N is the value set to the N-scale counter 184, fpls is thefrequency of the pulse output from the clock generator 188, and fdrv isthe frequency of the signal supplied to the piezoelectric elements 120 aand 120 b.

The calculation based on Equation 7 is performed by the CPU (controlunit) of the Bucom 101.

If the dust filter 119 is vibrated at a frequency in the ultrasonicregion (i.e., 20 kHz or more), the operating state of the dust filter119 cannot be aurally discriminated, because most people cannot hearsound falling outside the range of about 20 to 20,000 Hz. This is whythe operation display LCD 129 or the operation display LED 130 has adisplay unit for showing how the dust filter 119 is operating, to theoperator of the digital camera 10. More precisely, in the digital camera10, the vibrating members (piezoelectric elements 120 a and 120 b)imparts vibration to the dust-screening member (dust filter 119) that isarranged in front of the CCD 117, can be vibrated and can transmitlight. In the digital camera 10, the display unit is operated ininterlock with the vibrating member drive circuit (i.e., dust filtercontrol circuit 121), thus informing how the dust filter 119 isoperating (later described in detail).

To explain the above-described characteristics in detail, the controlthe Bucom 101 performs will be described with reference to FIGS. 18A to22. FIGS. 18A and 18B show the flowchart that relates to the controlprogram, which the Bucom 101 starts executing when the power switch (notshown) provided on the body unit 100 of the camera 10 is turned on.

First, a process is performed to activate the digital camera 10 (StepS101). That is, the Bucom 101 control the power-supply circuit 135. Socontrolled, the power-supply circuit 135 supplies power to the othercircuit units of the digital camera 10. Further, the Bucom 101initializes the circuit components.

Next, the Bucom 101 calls a sub-routine “silent vibration,” vibratingthe dust filter 119, making no sound (that is, at a frequency fallingoutside the audible range) (Step S102). The “audible range” ranges fromabout 200 to 20,000 Hz, because most people can hear sound fallingwithin this range.

Steps S103 to 5124, which follow, make a group of steps that iscyclically repeated. That is, the Bucom 101 first detects whether anaccessory has been attached to, or detached from, the digital camera 10(Step S103). Whether the lens unit 200 (i.e., one of accessories), forexample, has been attached to the body unit 100 is detected. Thisdetection, e.g., attaching or detaching of the lens unit 200, isperformed as the Bucom 101 communicates with the Lucom 201.

If a specific accessory is detected to have been attached to the bodyunit 100 (YES in Step S104), the Bucom 101 calls a subroutine “silentvibration” and causes the dust filter 119 to vibrate silently (StepS105).

While an accessory, particularly the lens unit 200, remains not attachedto the body unit 100 that is the camera body, dust is likely to adhereto each lens, the dust filter 119, and the like. It is thereforedesirable to perform an operation of removing dust at the time when itis detected that the lens unit 200 is attached to the body unit 100. Itis highly possible that dust adheres as the outer air circulates in thebody unit 100 at the time a lens is exchanged with another. It istherefore advisable to remove dust when a lens is exchange with another.Then, it is determined that photography will be immediately performed,and the operation goes to Step S106.

If a specific accessory is not detected to have been attached to thebody unit 100 (NO in Step S104), the Bucom 101 goes to the next step,i.e., Step S106.

In Step S106, the Bucom 101 detects the state of a specific operationswitch that the digital camera 10 has.

That is, the Bucom 101 determines whether the first release switch (notshown), which is a release switch, has been operated from the on/offstate of the switch (Step S107). The Bucom 101 reads the state. If thefirst release switch has not been turned on for a predetermined time,the Bucom 101 discriminates the state of the power switch (Step S108).If the power switch is on, the Bucom 101 returns to Step S103. If thepower switch is off, the Bucom 101 performs an end-operation (e.g.,sleep).

On the other hand, the first release switch may be found to have beenturned on in Step S107. In this case, the Bucom 101 acquires theluminance data about the object, from the photometry circuit 115, andcalculates from this data an exposure time (Tv value) and a diaphragmvalue (Av value) that are optimal for the image acquisition unit 116 andlens unit 200, respectively (Step S109).

Thereafter, the Bucom 101 acquires the detection data from the AF sensorunit 109 through the AF sensor drive circuit 110, and calculates adefocus value from the detection data (Step S110). The Bucom 101 thendetermines whether the defocus value, thus calculated, falls within apreset tolerance range (Step S111). If the defocus value does not fallwithin the tolerance range, the Bucom 101 drives the photographic lens202 (Step S112) and returns to Step S103.

On the other hand, the defocus value may falls within the tolerancerange. In this case, the Bucom 101 calls the subroutine “silentvibration” and causes the dust filter 119 to vibrate silently (StepS113).

Further, the Bucom 101 determines whether the second release switch (notshown), which is another release switch, has been operated (Step S114).If the second release switch is on, the Bucom 101 goes to Step S115 andstarts the prescribed photographic operation (later described indetail). If the second release switch is off, the Bucom 101 returns toStep S108.

During the image acquisition operation, the electronic image acquisitionis controlled for a time that corresponds to the preset time forexposure (i.e., exposure time), as in ordinary photography.

As the above-mentioned photographic operation, Steps S115 to S121 areperformed in a prescribed order to photograph an object. First, theBucom 101 transmits the Av value to the Lucom 201, instructing the Lucom201 to drive the diaphragm 203 (Step S115). Thereafter, the Bucom 101moves the quick return mirror 105 to the up position (Step S116). Then,the Bucom 101 causes the front curtain of the shutter 108 to startrunning, performing open control (Step S117). Further, the Bucom 101makes the image process controller 126 perform “image acquisitionoperation” (Step S118). When the exposure to the CCD 117 (i.e.,photography) for the time corresponding to the Tv value ends, the Bucom101 causes the rear curtain of the shutter 108 to start running,achieving CLOSE control (Step S119). Then, the Bucom 101 drives thequick return mirror 105 to the down position and cocks the shutter 108(Step S120).

Then, the Bucom 101 instructs the Lucom 210 to move the diaphragm 203back to the open position (Step S121). Thus, a sequence of imageacquisition steps is terminated.

Next, the Bucom 101 determines whether the recording medium 127 isattached to the body unit 100 (Step S122). If the recording medium 127is not attached, the Bucom 101 displays an alarm (Step S123). The Bucom101 then returns to Step S103 and repeats a similar sequence of steps.

If the recording medium 127 is attached, the Bucom 101 instructs theimage process controller 126 to record the image data acquired byphotography, in the recording medium 127 (Step S124). When the imagedata is completely recorded, the Bucom 101 returns to Step S103 againand repeats a similar sequence of steps.

In regard to the detailed relation between the vibration state and thedisplaying state will be explained in detail, the sequence ofcontrolling the “silent vibration” subroutine will be explained withreference to FIGS. 19 to 22. The term “vibration state” means the stateof the vibration induced by the piezoelectric elements 120 a and 120 b,i.e., vibrating members. FIG. 23 shows the form of a resonance-frequencywave that is continuously supplied to the vibrating members duringsilent vibration. The subroutine of FIG. 19, i.e., “silent vibration,”and the subroutine of FIGS. 20 to 22, i.e., “display process” areroutines for accomplishing vibration exclusively for removing dust fromthe dust filter 119. Vibrational frequency f₀ is set to a value close tothe resonance frequency of the dust filter 119. In the vibrational modeof FIG. 4A, for example, the vibrational frequency is 91 kHz, higherthan at least 20 kHz, and produces sound not audible to the user.

As shown in FIG. 19, when the “silent vibration” is called, the Bucom101 first reads the data representing the drive time (Toscf0) and drivefrequency (resonance frequency: Noscf0) from the data stored in aspecific area of the nonvolatile memory 128 (Step S201). At this timing,the Bucom 101 causes the display unit provided in the operation displayLCD 129 or operation display LED 130 to turn on the vibrational modedisplay, as shown in FIG. 20 (Step S301). The Bucom 101 then determineswhether a predetermined time has passed (Step S302). If thepredetermined time has not passed, the Bucom 101 makes the display unitkeep turning on the vibrational mode display. Upon lapse of thepredetermined time, the Bucom 101 turns off the displaying of thevibrational mode display (Step S303).

Next, the Bucom 101 outputs the drive frequency Noscf0 from the outputport D_NCnt to the N-scale counter 184 of the dust filter controlcircuit 121 (Step S202).

In the following steps S203 to 5205, the dust is removed as will bedescribed below. First, the Bucom 101 sets the output port P_PwCont toHigh, thereby starting the dust removal (Step S203). At this timing, theBucom 101 starts displaying the vibrating operation as shown in FIG. 21(Step S311). The Bucom 101 then determines whether or not thepredetermined time has passed (Step S312). If the predetermined time hasnot passed, the Bucom 101 keeps displaying the vibrating operation. Uponlapse of the predetermined time, the Bucom 101 stops displaying of thevibrating operation (Step S313). The display of the vibrating operation,at this time, changes as the time passes or as the dust is removed (howit changes is not shown, though). The predetermined time is almost equalto Toscf0, i.e., the time for which the vibration (later described)continues.

If the output port P_PwCont is set to High in Step S203, thepiezoelectric elements 120 a and 120 b vibrate the dust filter 119 atthe prescribed vibrational frequency (Noscf0), removing the dust 181from the surface of the dust filter 119. At the same time the dust isremoved from the surface of the dust filter 119, air is vibrated,producing an ultrasonic wave. The vibration at the drive frequencyNoscf0, however, does not make sound audible to most people. Hence, theuser hears nothing. The Bucom 101 waits for the predetermined timeToscf0, while the dust filter 119 remains vibrated (Step S204). Uponlapse of the predetermined time Toscf0, the Bucom 101 sets the outputport P_PwCont to Low, stopping the dust removal operation (Step S205).At this timing, the Bucom 101 turns on the display unit, whereby thedisplaying of the vibration-end display is turned on (Step S321). Whenthe Bucom 101 determines (in Step S322) that the predetermined time haspassed, the displaying of the vibration-end display is turned off (StepS323). The Bucom 101 then returns to the step next to the step in whichthe “silent vibration” is called.

The vibrational frequency f₀ (i.e., resonance frequency Noscf0) and thedrive time (Toscf0) used in this subroutine define such a waveform asshown in the graph of FIG. 23. As can be seen from this waveform,constant vibration (f₀=91 kHz) continues for a time (i.e., Toscf0) thatis long enough to accomplish the dust removal.

That is, the vibrational mode adjusts the resonance frequency applied tothe vibrating member, controlling the dust removal.

Second Embodiment

The subroutine “silent vibration” called in the camera sequence (mainroutine) that the Bucom performs in a digital camera that is a secondembodiment of the image equipment according to this invention will bedescribed with reference to FIG. 24. FIG. 24 illustrates a modificationof the subroutine “silent vibration” shown in FIG. 19. The secondembodiment differs from the first embodiment in the operating mode ofthe dust filter 119. In the first embodiment, the dust filter 119 isdriven at a fixed frequency, i.e., frequency f₀, producing a standingwave. By contrast, in the second embodiment, the drive frequency isgradually changed, thereby achieving large-amplitude vibration atvarious frequencies including the resonance frequency, without strictlycontrolling the drive frequency.

If the aspect ratio of the dust filter 119 changes from the design valueduring the manufacture, the vibration speed will change (sharplydecreasing the vibration speed ratio as seen from FIG. 10). Further, thelengths of the piezoelectric elements 120 a and 120 b may change, too,from the design value during the manufacturing. In this case, thevibration speed ratio will change (see FIG. 11). Moreover, the vibrationspeed changes even if the vibrator 155 is held and supported (as shownin FIG. 7). Therefore, a precise resonance frequency must be set in eachproduct and the piezoelectric elements 120 a and 120 b must be driven atthe frequency so set. This is because the vibration speed will furtherdecrease if the piezoelectric elements are driven at any frequency otherthan the resonance frequency. An extremely simple circuit configurationcan, nonetheless, drive the piezoelectric elements precisely at theresonance frequency if the frequency is controlled as in the secondembodiment. A method of control can therefore be achieved to eliminateany difference in resonance frequency between the products.

In the subroutine “silent vibration” of FIG. 24, the vibrationalfrequency f₀ is set to a value close to the resonance frequency of thedust filter 119. The vibrational frequency f₀ is 91 kHz in, for example,the vibrational mode of FIG. 4A. That is, the vibrational frequencyexceeds at least 20 kHz, and makes sound not audible to the user.

First, the Bucom 101 reads the data representing the drive time(Toscf0), drive-start frequency (Noscfs), frequency change value (Δf)and drive-end frequency (Noscft), from the data stored in a specificarea of the nonvolatile memory 128 (Step S211). At this timing, theBucom 101 causes the display unit to display the vibrational mode asshown in FIG. 20, in the same way as in the first embodiment.

Next, the Bucom 101 sets the drive-start frequency (Noscfs) as drivefrequency (Noscf) (Step S212). The Bucom 101 then outputs the drivefrequency (Noscf) from the output port D_NCnt to the N-scale counter 184of the dust filter control circuit 121 (Step S213).

In the following steps S203 et seq., the dust is removed as will bedescribed below. First, the dust removal is started. At this time, thedisplay of the vibrating operation is performed as shown in FIG. 21, asin the first embodiment.

First, the Bucom 101 sets the output port P_PwCont to High, to achievedust removal (Step S203). The piezoelectric elements 120 a and 120 bvibrate the dust filter 119 at the prescribed vibrational frequency(Noscf), producing a standing wave of a small amplitude at the dustfilter 119. The dust cannot be removed from the surface of the dustfilter 119, because the vibrational amplitude is small. This vibrationcontinues for the drive time (Toscf0) (Step S204). Upon lapse of thisdrive time (Toscf0), the Bucom 101 determines whether the drivefrequency (Noscf) is equal to the drive-end frequency (Noscft) (StepS214). If the drive frequency is not equal to the drive-end frequency(NO in Step S214), the Bucom 101 adds the frequency change value (Δf) tothe drive frequency (Noscf), and sets the sum to the drive frequency(Noscf) (Step S215). Then, the Bucom 101 repeats the sequence of StepsS212 to S214.

If the drive frequency (Noscf) is equal to the drive-end frequency(Noscft) (YES in Step S214), the Bucom 101 sets the output port P_PwContto Low, stopping the vibration of the piezoelectric elements 120 a and120 b (Step S205), thereby terminating the “silent vibration.” At thispoint, the display of vibration-end is performed as shown in FIG. 22, asin the first embodiment.

As the frequency is gradually changed as described above, the amplitudeof the standing wave increases. In view of this, the drive-startfrequency (Ncoscfs), the frequency change value (Δf) and the drive-endfrequency (Noscft) are set so that the resonance frequency of thestanding wave may be surpassed. As a result, a standing wave of smallvibrational amplitude is produced at the dust filter 119. The standingwave can thereby controlled, such that its vibrational amplitudegradually increases until it becomes resonance vibration, and thendecreases thereafter. If the vibrational amplitude (corresponding tovibration speed) is larger than a prescribed value, the dust 181 can beremoved. In other words, the dust 181 can be removed while thevibrational frequency remains in a prescribed range. This range is broadin the present embodiment, because the vibrational amplitude is largeduring the resonance.

If the difference between the drive-start frequency (Noscfs) and thedrive-end frequency (Noscft) is large, the fluctuation of the resonancefrequency, due to the temperature of the vibrator 155 or to thedeviation in characteristic change of the vibrator 155, during themanufacture, can be absorbed. Hence, the dust 181 can be reliablyremoved from the dust filter 119, by using an extremely simple circuitconfiguration.

The present invention has been explained, describing some embodiments.Nonetheless, this invention is not limited to the embodiments describedabove. Various changes and modifications can, of course, be made withinthe scope and spirit of the invention.

In the embodiment described above, for example, the cushion members 152and 153 are arranged on the circle 154 concentric to the center O of thevibrator 155 that includes the dust filter 119 and the piezoelectricelements 120 a and 120 b. Nonetheless, the cushion members 152 and 153,which are used as hold and support member, can be arranged on an ellipseor quasi-circular closed loop that is concentric to the center O of thevibrator 155. In this case, too, almost the same advantage as mentionedabove can be achieved.

A mechanism that applies an air flow or a mechanism that has a wipe maybe used in combination with the dust removal mechanism having thevibrating member, in order to remove the dust 181 from the dust filter119.

In the embodiments described above, the vibrating members arepiezoelectric elements. The piezoelectric elements may be replaced byelectrostrictive members or super magnetostrictive elements. In theembodiments, two piezoelectric elements 120 a and 120 b are secured tothe dust filter 119 that is dust-screening member. Instead, only onepiezoelectric element may be secured to the dust filter 119. In thiscase, that side of the dust filter 119, to which the piezoelectricelement is secured, differs in rigidity from the other side of the dustfilter 119. Consequently, the node areas 175 where vibrational amplitudeis small will form a pattern similar to that of FIG. 4A, FIG. 8 or FIG.9, but will be dislocated. Thus, it is desirable to arrange twopiezoelectric elements symmetrical to each other, because the vibrationcan be produced more efficiently and the dust filter 119 can be moreeasily held at four corners.

In order to remove dust more efficiently from the member vibrated, themember may be coated with an indium-tin oxide (ITO) film, which is atransparent conductive film, indium-zinc film, poly 3,4-ethylenedioxythiophene film, surfactant agent film that is a hygroscopicanti-electrostatic film, siloxane-based film, or the like. In this case,the frequency, the drive time, etc., all related to the vibration, areset to values that accord with the material of the film.

Moreover, the optical LPF 118, described as one embodiment of theinvention, may be replaced by a plurality of optical LPFs that exhibitbirefringence. Of these optical LPFs, the optical LPF located closest tothe object of photography may be used as a dust-screening member (i.e.,a subject to be vibrated), in place of the dust filter 119 shown in FIG.2A.

Further, a camera may does not have the optical LPF 118 of FIG. 2Adescribed as one embodiment of the invention, and the dust filter 119may be used as an optical element such as an optical LPF, aninfrared-beam filter, a deflection filter, or a half mirror.

Furthermore, the camera may not have the optical LPF 118, and the dustfilter 119 may be replaced by the protection glass plate 142 shown inFIG. 2A. In this case, the protection glass plate 142 and the CCD chip136 remain free of dust and moisture, and the structure of FIG. 2A thatsupports and yet vibrates the dust filter 119 may be used to support andvibrate the protection glass plate 142. Needless to say, the protectionglass plate 142 may be used as an optical element such as an opticalLPF, an infrared-beam filter, a deflection filter, or a half mirror.

The image equipment according to this invention is not limited to theimage acquisition apparatus (digital camera) exemplified above. Thisinvention can be applied to any other apparatus that needs a dustremoval function. The invention can be practiced in the form of variousmodifications, if necessary. More specifically, a dust moving mechanismaccording to this invention may be arranged between the display elementand the light source or image projecting lens in an image projector.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A vibrating device comprising: a vibrator including: a dust-screeningmember which is shaped like a plate as a whole and has at least one sidethat is symmetric with respect to a symmetry axis; and a vibratingmember secured to the dust-screening member and configured to produce,at the dust-screening member, vibration having a vibrational amplitudeperpendicular to a surface of the dust-screening member; and a hold andsupport member configured to hold and support the vibrator to a fixedmember, wherein the hold and support position by the hold and supportmember is arranged at position along a circle or ellipse concentric tothe centroid of the vibrator such that peak ridges of the vibrationhaving a vibrational amplitude perpendicular to the surface of thedust-screening member form closed loops.
 2. The device according toclaim 1, further comprising: a drive unit configured to drive thevibrating member to produce vibration Z (x, y) at the dust-screeningmember, the vibration being expressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{mn}( {x,y} )} = {{\sin ( {{n\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{m\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};$${{W_{nm}( {x,y} )} = {{\sin ( {{m\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{n\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};{and}$γ is +Π/4 or ranges from −Π/8 to −Π/4, wherein the device has such asize that LP/LF is 0.5 or more, but less than 1, where LF is the lengthof the sides to which the vibrating member is arranged in a virtualrectangle having the same area as the surface of the dust-screeningmember and sides including the one side, and LB is the longitudinallength of the vibrating member of the sides parallel to the one side. 3.The device according to claim 1, wherein the dust-screening membercoincides with the virtual rectangle when the dust-screening member isrectangular.
 4. The device according to claim 2, wherein thedust-screening member has such a size that the ratio of the length ofthe sides orthogonal to the sides to which the vibrating member isarranged to the length of the vibrating member arranged sides in thevirtual rectangle is 0.9 or more, but less than
 1. 5. The deviceaccording to claim 2, wherein γ is +Π/4, and the vibration produced atthe dust-screening member by the drive unit is vibration such that peakridges of the vibration having a vibrational amplitude perpendicular tothe surface of the dust-screening member form closed loops.
 6. Thedevice according to claim 2, wherein γ ranges from −Π/8 to −Π/4, and thevibration produced at the dust-screening member by the drive unit isvibration such that peak ridges of the vibration having a vibrationalamplitude perpendicular to the surface of the dust-screening member formcurves around a midpoint of the side which the dust-screening memberhas.
 7. The device according to claim 2, wherein the vibrating memberincludes a piezoelectric element, and the drive unit is configured tosupply a signal to the piezoelectric element to produce the vibration atthe dust-screening member, the signal having a frequency that accordswith a size and material of the dust-screening member.
 8. The deviceaccording to claim 7, wherein the drive unit configured to supply asignal to the piezoelectric element at prescribed time intervals, thesignal changing in frequency, from a drive-start frequency to adrive-end frequency in increments of a given transmutation frequency,including the frequency that accords with the with size and material ofthe dust-screening member.
 9. The device according to claim 2, wherein aplurality of vibrating members are provided on the dust-screeningmember.
 10. An image equipment comprising: an image forming elementhaving an image surface on which an optical image is formed; a vibratorincluding: a dust-screening member which is shaped like a plate as awhole, has at least one side that is symmetric with respect to asymmetry axis, and has a light-transmitting region at least spreading toa predetermined region, facing the image surface and spaced therefrom bya predetermined distance; and a vibrating member configured to producevibration having an amplitude perpendicular to a surface of thedust-screening member, the vibrating member being provided on thedust-screening member, outside the light-transmitting region throughwhich a light beam forming an optical image on the image surface passes;a sealing structure for surrounding the image forming element and thedust-screening member, thereby providing a closed space in which theimage forming element and the dust-screening member that face eachother; and a hold and support member configured to hold and support thevibrator to the sealing structure, wherein the hold and support positionby the hold and support member is arranged at position along a circle orellipse concentric to the centroid of the vibrator such that peak ridgesof the vibration having a vibrational amplitude perpendicular to thesurface of the dust-screening member form closed loops.
 11. Theequipment according to claim 10, further comprising: a drive unitconfigured to drive the vibrating member to produce vibration Z (x, y)at the dust-screening member, the vibration being expressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{mn}( {x,y} )} = {{\sin ( {{n\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{m\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};$${{W_{nm}( {x,y} )} = {{\sin ( {{m\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{n\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};{and}$γ is +Π/4 or ranges from −Π/8 to −Π/4, wherein the equipment has such asize that LP/LF is 0.5 or more, but less than 1, where LF is the lengthof the sides to which the vibrating member is arranged in a virtualrectangle having the same area as the surface of the dust-screeningmember and sides including the one side, and LB is the longitudinallength of the vibrating member of the sides parallel to the one side.12. The equipment according to claim 10, wherein the dust-screeningmember coincides with the virtual rectangle when the dust-screeningmember is rectangular.
 13. The equipment according to claim 10, whereinthe dust-screening member has such a size that the ratio of the lengthof the sides orthogonal to the sides to which the vibrating member isarranged to the length of the vibrating member arranged sides in thevirtual rectangle is 0.9 or more, but less than
 1. 14. The equipmentaccording to claim 11, wherein γ is +Π/4, and the drive unit produces atthe dust-screening member vibration such that peak ridges of thevibration having a vibrational amplitude perpendicular to the surface ofthe dust-screening member form closed loops around an optical axis thatpasses the image surface of the image forming element.
 15. The equipmentaccording to claim 14, wherein the sealing structure includes a holderarranged so as to achieve airtight sealing between the image formingelement and the dust-screening member, and the hold and support memberincludes a support member configured to secure the dust-screening memberto the holder, the support member being arranged in a node region thathas almost no vibrational amplitude perpendicular to a surface of thedust-screening member.
 16. The equipment according to claim 11, whereinγ is −Π/8 to −Π/4, and the drive unit produces at the dust-screeningmember vibration such that peak ridges of the vibration having avibrational amplitude perpendicular to the surface of the dust-screeningmember form curves surrounding a midpoint of the side which thedust-screening member has.
 17. The equipment according to claim 16,wherein the sealing structure includes a holder arranged so as toachieve airtight sealing between the image forming element and thedust-screening member, and the hold and support member includes asupport member configured to secure the dust-screening member to theholder, the support member being arranged in a node region that hasalmost no vibrational amplitude perpendicular to a surface of thedust-screening member.
 18. The equipment according to claim 11, whereinthe vibrating member includes a piezoelectric element, and the driveunit configured to supply a signal to the piezoelectric element toproduce the vibration at the dust-screening member, the signal having afrequency that accords with a size and material of the dust-screeningmember.
 19. The equipment according to claim 18, wherein the drive unitconfigured to supply a signal to the piezoelectric element at prescribedtime intervals, the signal changing in frequency, from a drive-startfrequency to a drive-end frequency in increments of a giventransmutation frequency, including the frequency that accords with thewith size and material of the dust-screening member.
 20. The equipmentaccording to one of claims 10 to 13, wherein vibrating members includingthe vibrating member are opposed across a transmission region of thedust-screening member, through which light passes.